When unilateral or asymmetric lung injuries are treated with conventional respiratory therapy, the results can be very unsatisfactory. At times it becomes necessary to separate the two lungs with an endobronchial tube and treat each lung individually. Though differential lung ventilation is used in many centers, little is known about how to divide the tidal volumes and adjust airway pressures in the two lungs to obtain the best outcome. Our work in dogs has shown that expiratory airway pressure (PEEP) allocation is critical. Oxygenation is profoundly better if PEEP levels are properly chosen. This proposal is aimed at defining the consequences of unilateral PEEP allocation during differential ventilation. Using an asymmetric pulmonary injury dog model, PEEP will be given in increments while outcome is measured in terms of shunt, PaO2, and gas exchange. Procedures will be introduced which are expected to alter the optimum PEEP allocation, changes in body position and vasoactive drugs, and the studies repeated. We expect the results from this project will define criteria for PEEP allocation during the acute phase following asymmetric pulmonary injury. Once techniques are found to optimize PEEP we plan to extend these results to a much wider population by studying diffuse bilateral pulmonary disease. The PEEP allocation results will be applied to a porcein model of diffuse injury. It will be determined it position induced changes in ventilation-perfusion can be reversed by unilateral PEEP. Further investigation will examine the use of asynchronous differential ventilation (ventilators 180 degrees out of phase) to lower mean airway pressure and reduce the adverse effects of PEEP in treatment of diffuse disease.